1. Field of the Invention
The present invention relates to fabrication of a thin film pattern of a display panel, and more particularly, to an apparatus for fabricating a thin film pattern, in which cost savings may be realized due to prolongation of a blanket lifespan and reliability of the thin film pattern may be improved, and a method for fabricating the thin film pattern with the apparatus.
2. Discussion of the Related Art
Recently, a variety of flat panel displays capable of relieving disadvantages, e.g., heaviness and bulkiness, of cathode ray tubes (CRTs), have drawn a great deal of attention. Examples of flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs) and electro-luminescent displays (ELDs).
Of these, LCDs control light transmittance of liquid crystal by an electric field to display an image. In order to realize such a mechanism, LCDs include a LCD panel, where LCD cells are arranged in the form of an active matrix, and driving circuits to drive the LCD panel.
The LCD panel includes: a thin film transistor array substrate and a color filter array substrate arranged such that they face each other; and a spacer arranged between the two substrates to maintain a cell gap; and a liquid crystal sealing the cell gap.
The thin film transistor array substrate includes a plurality of gate lines and a plurality of data lines, a thin film transistor formed as a switching element at an intersection between each of the gate lines and each of the data lines, a pixel electrode in contact with the thin film transistor at each of liquid crystal cells, and an alignment film arranged over the entire surface of the thin film transistor array substrate including the resulting structure. The gate and data lines receive a signal through respective pad parts from the driving circuits. The thin film transistor supplies a pixel signal through a data line to the pixel electrode in response to a scanning signal received through the gate line.
The color filter array substrate includes a plurality of color filters arranged at respective liquid crystal cells, a black matrix to partition the color filters and reflect external light, a common electrode to commonly supply a reference voltage to the liquid crystal cells, and an alignment film arranged over the entire surface of the color filter array substrate including the resulting structure.
The thin film transistor array substrate and color filter array substrate are separately formed and joined to each other, and a liquid crystal is inserted between the two substrates and then sealed, to complete fabrication of an LCD panel.
In the related art, thin film patterns in a LCD panel are formed through photolithographic and etching processes. However, photolithographic processes involve a series of steps such as exposing, developing, cleaning and testing, thus making LCD fabrication costs expensive. Accordingly, reverse resist printing is recently used in the related art to pattern thin films, instead of the photolithographic process.
According to the reverse resist printing, an etch-resist solution is coated on a blanket wound around a printing roller of an etch-resist solution injection apparatus and transferred to a protrusion only of a printing plate. Thus, the etch-resist solution is left on the printing roller having a desired thin film pattern, and the etch-resist pattern is then transferred to a substrate to fabricate the thin film pattern on the substrate. The etch-resist solution used for the reverse resist printing consists of a base polymer such as novolac, a carrier solvent, a printing solvent and a surfactant.
The carrier solvent is a solvent used to lower the viscosity of the etch-resist solution discharged from the injection apparatus thereby allowing the etch-resist solution to be uniformly coated on the blanket.
The printing solvent imparts tackiness or stickiness to the etch-resist solution coated on the blanket, in order to allow the etch-resist solution to be efficiently coated on a printing plate or substrate.
The surfactant is a substance which readily adheres to an interface and greatly lowers surface tension with the interface, and is used herein to lower surface tension of the etch-resist solution.
As shown in FIG. 1, when coated on a printing roller, the etch-resist solution is liquid. At this time, the etch-resist solution can be uniformly coated on the blanket of the printing roller, due to the carrier solvent contained therein. Then, the highly volatile carrier solvent is removed from the etch-resist solution. As a result, the etch-resist solution undergoes phase-transition from liquid to gel.
Then, in a printing process, the printing solvent is gradually removed, and the etch-resist is formed on the substrate, and is then subjected to curing and baking. As a result, the etch-resist is solidified.
Accordingly, the carrier solvent is removed immediately after coating, but the printing solvent remains on the etch-resist and permeates into the blanket during printing. As a result, swelling of the blanket (hereinafter, referred to as “swelling”) occurs, which greatly prevents the etch-resist from being normally formed on the substrate, as shown in FIG. 2. Accordingly, problems occur, e.g., severe deterioration in reliability of thin film pattern formation and in blanket lifespan.